1. Field of the Invention
The present invention relates to a liquid discharge head for discharging liquid and the driving method therefor, and a cartridge formed integrally with a liquid tank retaining liquid to be supplied to the liquid discharge head. The invention also relates to an image forming apparatus to form images on a printing medium. The invention is not only applicable to the printing apparatuses generally in use, but also, to a copying machine, a facsimile equipment provided with communication systems, and an apparatus having a printing unit, such a word processor. Further, the invention is applicable to an industrial recording system having various processing apparatuses complexly combined therein, as well as to a textile printing apparatus and a processing apparatus such as to perform etching or the like.
Here, the term xe2x80x9cprintingxe2x80x9d or xe2x80x9crecordingxe2x80x9d used for the specification hereof means not only the formation of characters, graphics, and other meaningful information, but also, it is meant to include, in a broad sense, images, designs, patterns, or the like formed on a printing medium, and also, to include processes such as etching, irrespective of being meaningful or otherwise, or being apparent to be visually recognizable by eyesight.
Also, the term xe2x80x9cprinting mediumxe2x80x9d means not only the paper sheet that is usually used for a printing apparatus in general, but it means cloth, plastic film, metallic plate, glass, ceramic, wood, leather, or the like, which is capable of receiving ink. Also, the printing medium may be a three-dimensional object, such as a spherical or cylindrical one, besides the one in the form of a sheet.
Further, the term xe2x80x9cliquidxe2x80x9d should also be interpreted in a broad sense as in the definition of the xe2x80x9cprinting (or recording)xe2x80x9d as described above, and it is meant to include the one used for a printing medium to form images, designs, patterns, or the like, or used for etching process of a printing medium or ink processing (such as coagulating or insolubilizing coloring materials in ink to be used for a printing medium).
2. Related Background Art
For the liquid jet discharging method of ink jet type which is generally in use at present, there have been known the method that utilizes electrothermal transducing elements (heaters) as discharge energy generating elements used for discharging ink or the processing liquid which is used for adjusting the printability of ink on a printing medium (hereinafter referred to as collectively xe2x80x9cinkxe2x80x9d or xe2x80x9cliquidxe2x80x9d for the convenience"" sake in the specification hereof), and the method that utilizes piezoelectric elements (piezo). Both of them make it possible to control the discharges of liquid droplets by the application of electric signals.
Now, for example, the principle of ink discharging method that uses electrothermal transducing elements is that with the application of electric signals to the electrothermal transducing elements, film boiling is created in ink instantaneously in the vicinity of the electrothermal transducing elements, and that ink droplets are discharged at high speed by the abrupt development of a bubble created by the phase changes of ink at that time. On the other hand, the principle of method for discharging ink droplets by use of piezoelectric elements is that with the displacement of piezoelectric elements by the application of electric signals, ink droplets are discharged by the pressure exerted when such displacement is effectuated.
Here, for the former method, there are advantages, among some others, that the space needed to provide the discharge energy generating elements can be smaller; the structure of ink jet head is made simpler; and the integration of nozzles is easer. However, as the characteristic drawback of this method, the voluminal changes of flying ink droplets may ensue from the accumulation of heat in the ink jet head due to heat generated by electrothermal transducing elements, and the electrothermal transducing elements are subjected to being affected by cavitation that may be brought about at the time of debubbling.
As one of the methods to solve the drawback described above, there are disclosed an ink jet printing method and an ink jet head in the specification of Japanese Patent Application Laid-Open No. 04-10941. The ink jet head disclosed in the specification thereof is provided with discharge ports for discharging ink, ink flow paths filled with ink, which is communicated with the discharge ports, and the electrothermal transducing elements formed with thin film resistive elements provided for ink flow paths to generate thermal energy. Then, when driving pulses are applied to them through electric wiring, thermal energy is generated, and the film boiling, which has been crated by the thermal energy, is developed. Then, utilizing the pressure of a bubble thus created ink droplets are discharged from the discharge ports. At this juncture, a bubble is communicated with the air outside. With this printing method, it becomes possible to stabilize the volume of flying ink droplets; to perform high speed printing using extremely fine ink droplets; and to enhance the durability of electrothermal transducing elements by eliminating cavitation at the time of debubbling. In this way, highly precise images can be obtained more easily.
One of the objects of the present invention is to attempt a further improvement of a liquid discharge head for discharging liquid by use of a bubble created by thermal energy, which enables a bubble to be communicated with the air outside, and also, the driving method therefor, a cartridge, and an image forming apparatus as well.
Another object of the invention is to provide a liquid discharge head for discharging liquid by use of a bubble created by thermal energy, which is capable of reducing unexpected non-discharges and the remaining bubble in a liquid chamber so as to discharge liquid stably from the discharge ports as droplets for the enhancement of displacement accuracy of the liquid droplets on a printing medium, hence performing high quality printing with excellent viscous plug properties, as well as to provide the driving method therefor, a cartridge, and an image forming apparatus.
It is still another object of the invention to provide a liquid discharge head which comprises discharge ports for discharging liquid; electrothermal transducing elements arranged to face the discharge ports for generating thermal energy utilized for discharging liquid from the discharge ports; and a covering layer for covering the electrothermal transducing element, residing inclusively between the electrothermal transducing element and liquid. For this liquid discharge head, the gap between the discharge port and the surface of the covering layer is 34 xcexcm or less, and the thickness of the covering layer is 6,300 xc3x85 or less, and then, the electrothermal transducing element generates thermal energy of 0.0027 xcexcJ/xcexcm2 or less by the application of single driving pulse of 1.2 xcexcs or less for creating film boiling in liquid to discharge liquid from the discharge port.
It is a further object of the invention to provide a liquid discharge head which comprises discharge ports for discharging liquid; and electrothermal transducing elements for generating thermal energy utilized for discharging liquid from the discharge ports, the electrothermal transducing elements being directly in contact with liquid. For this liquid discharge head, the gap between the discharge port and the surface of the covering layer is 34 xcexcm or less, and the electrothermal transducing element generates thermal energy of 0.0027 xcexcJ/xcexcm2 or less by the application of single driving pulse of 1.2 xcexcs or less for creating film boiling in liquid to discharge liquid from the discharge port.
It is a further object of the invention to provide a method for driving a liquid discharge head having discharge ports for discharging liquid; electrothermal transducing elements arranged to face the discharge ports for generating thermal energy utilized for discharging liquid from the discharge ports; and a covering layer for covering the electrothermal transducing element, residing inclusively between the electrothermal transducing element and liquid, the gap between the discharge port and the surface of the covering layer being 34 xcexcm or less, and the thickness of the covering layer being 6,300 xc3x85 or less, which comprises the step of applying single driving pulse of 1.2 xcexcs or less to the electrothermal transducing element for generating thermal energy of 0.0027 xcexcJ/xcexcm2 or less to create film boiling in liquid for discharging liquid from the discharge port.
It is still a further object of the invention to provide a method for driving a liquid discharge head having discharge ports for discharging liquid; and electrothermal transducing elements for generating thermal energy utilized for discharging liquid from the discharge ports, the electrothermal transducing elements being directly in contact with liquid, and the gap between the discharge port and the surface of the covering layer being 34 xcexcm or less, which comprises the step of applying single driving pulse of 1.2 xcexcs or less to the electrothermal transducing element for generating thermal energy of 0.0027 xcexcJ/xcexcm2 or less to create boiling in liquid for discharging liquid from the discharge port.
It is another object of the invention to provide a cartridge which comprises a liquid discharge head provided with discharge ports for discharging liquid; electrothermal transducing elements arranged to face the discharge ports for generating thermal energy utilized for discharging liquid from the discharge ports; and a covering layer for covering the electrothermal transducing element, residing inclusively between the electrothermal transducing element and liquid, the gap between the discharge port and the surface of the covering layer being 34 xcexcm or less, and the thickness of the covering layer being 6,300 xc3x85 or less, and by applying single driving pulse of 1.2 xcexcs or less to the electrothermal transducing element for generating thermal energy of 0.0027 xcexcJ/xcexcm2 or less to create film boiling in liquid for discharging liquid from the discharge port; and a liquid tank for storing liquid to be supplied to the liquid discharge head.
Also, it is another object of the invention to provide cartridge which comprises a liquid discharge head provided with discharge ports for discharging liquid; and electrothermal transducing elements for generating thermal energy utilized for discharging liquid from the discharge ports, the electrothermal transducing elements being directly in contact with liquid, and the gap between the discharge port and the surface of the covering layer being 34 xcexcm or less, and by applying single driving pulse of 1.2 xcexcs or less to the electrothermal transducing element for generating thermal energy of 0.0027 xcexcJ/xcexcm2 or less to create boiling in liquid for discharging liquid from the discharge port; and a liquid tank for storing liquid to be supplied to the liquid discharge head.
Also, it is another object of the invention to provide an image forming apparatus which comprises a liquid discharge head provided with discharge ports for discharging liquid; electrothermal transducing elements arranged to face the discharge ports for generating thermal energy utilized for discharging liquid from the discharge ports; a covering layer for covering the electrothermal transducing element, residing inclusively between the electrothermal transducing element and liquid, the gap between the discharge port and the surface of the covering layer being 34 xcexcm or less, and the thickness of the covering layer being 6,300 xc3x85 or less; and a control unit for applying single driving pulse of 1.2 xcexcs or less to the electrothermal transducing element for generating thermal energy of 0.0027 xcexcJ/xcexcm2 or less to create film boiling in liquid for discharging liquid from the discharge port.
Also, it is another object of the invention to provide an image forming apparatus which comprises a liquid discharge head provided with discharge ports for discharging liquid; and electrothermal transducing elements for generating thermal energy utilized for discharging liquid from the discharge ports, the electrothermal transducing elements being directly in contact with liquid, and the gap between the discharge port and the surface of the covering layer being 34 xcexcm or less; and a control unit for applying single driving pulse of 1.2 xcexcs or less to the electrothermal transducing element for generating thermal energy of 0.0027 xcexcJ/xcexcm2 or less to create boiling in liquid for discharging liquid from the discharge port.
In accordance with the present invention, the gap between the discharge port and the electrothermal transducing element is 34 xcexcm or less, and also, the thickness of the covering layer is 6,300 xc3x85 or less. Then, by the application of single driving pulse of 1.2 xcexcs or less, thermal energy of 0.0027 xcexcJ/xcexcm2 or less is generated to create film boiling in liquid for discharging liquid from the discharge port. As a result, the fluctuation of liquid bubbling on the surface of the electrothermal transducing element is reduced to stabilize bubbling. Furthermore, since the resultant amount of meniscus retraction becomes smaller at the time of discharge, liquid can return to the surface of the electrothermal transducing element quicker so that meniscus faces the discharge port, hence making it possible to enhance the displacement accuracy of liquid droplets on a printing medium even when driving is executed at high frequency. Also, it becomes possible to reduce the electric power given to the electrothermal transducing element, which contributes to enabling meniscus to return quickly and face the discharge port. As a result, the wetted liquid on the discharge port surface is allowed to be combined with the liquid which is being refilled in the discharge port, which makes it possible to reduce the occurrence of unexpected non-discharges.
With the electrodermal transducing element being configured to be square, it becomes possible to enhance the viscous plug properties of ink droplets more if the distance L is made smaller by 1.3 times the length of one side of such electrothermal transducing element.
With the discharge ports arranged at least in two lines parallel to each other arranged at intervals of 600 dpi, respectively, it becomes possible to obtain a liquid discharge head whose performance is as high as 1,200 dpi if the arrangement pitches are deviated by half pitch from each other per line.
With the amount of discharge of liquid being 5 picoliters or less when discharged from the discharge port by the application of single driving pulse to the electrothermal transducing element, it becomes possible to enhance resolution of images for the significant improvement of the quality of images thus obtained.
With driving means of the liquid discharge head being provided with the base plate having wiring section formed on the electrothermal transducing element in the scanning movement direction of the carriage, it becomes possible to uniform the temperature distribution on the surface of each individual electrothermal transducing element in the arrangement direction of the discharge port, thus suppressing the inclination of discharge direction of liquid droplets in the arrangement direction of discharge ports, and preventing the occurrence of white streaks or the like.